Current wireless mobile communication devices include microprocessors, memory, soundcards, and run one or more software applications in addition to providing for voice communications. Examples of software applications used in these wireless devices include micro-browsers, address books, email clients, instant messaging (IM) clients, and wavetable instruments. Additionally, wireless devices have access to a plurality of services via the Internet. A wireless device may, for example, be used to browse web sites on the Internet, to transmit and receive graphics, and to execute streaming audio and/or video applications. The transfer of Internet content to and from wireless device is typically facilitated by the Wireless Application Protocol (WAP), which integrates the Internet and other networks with wireless network platforms. Such wireless devices may operate on a cellular network, on a wireless local area network (WLAN), or on both of these types of networks.
With respect to WLANs, the term “Wi-Fi” or Wireless Fidelity pertains to certain types of WLANs that use specifications in the Institute of Electrical and Electronics Engineers (“IEEE”) 802.11 family.
In a WLAN, an access point is a station that transmits and receives data (sometimes referred to as a transceiver). An Access Point in an infrastructure BSS (or a client node acting as an AP in an Independent BSS) connects users to other users within the network and also can serve as the point of interconnection between the WLAN and a wired LAN. Each access point can serve multiple users within a defined network area. As users move beyond the range of one access point (i.e., when they roam), they are automatically handed over to the next one. A small WLAN may only require a single access point. The number of access points required increases as a function of the number of network users and the physical size of the network. The access point is typically an IEEE 802.11 (i.e. WLAN) radio receiver/transmitter (or transceiver) and functions as a gateway or bridge between a WLAN and a wired LAN.
A block diagram illustrating an example wireless communications system is shown in FIG. 1. The example system, generally referenced 10, comprises one or more mobile devices 12 implementing a WLAN station connected to access point (AP) 14 which is connected to network 16. The system also comprises a cellular base station 20 in communication over an air interface to the mobile device. The base station is connected to a cellular network 22 which is also connected to network 16.
A service set identifier (SSID) identifies a particular IEEE 802.11 wireless LAN. A client device receives broadcast messages from all access points within range advertising their SSIDs. The client device can then either manually or automatically select the network with which to associate. It is legitimate for multiple access points to share the same SSID if they provide access to the same network as part of an extended service set.
The basic service set (BSS) is the basic building block of an IEEE 802.11 wireless LAN. In infrastructure mode one access point (AP) together with all associated stations (STAs) is called a BSS. An AP acts as a master to control the stations within that BSS. Each BSS is identified by a Basic Service Set Identifier (BSSID). The most basic BSS is two STAs in Independent mode. In infrastructure mode, a basic BSS consists of one AP and one STA. The BSSID uniquely identifies each BSS (the SSID however, can be used in multiple, possibly overlapping, BSSs). In an infrastructure BSS, the BSSID is the MAC address of the wireless access point (WAP).
When a station wants to access an existing BSS (such as after power-up, sleep mode or just entering a BSS area), the station must get synchronization information from the Access Point. The station obtains this information by either (1) passive scanning whereby the station waits to receive a Beacon frame (and/or Probe Responses sent in response to other stations' Probe Requests) from the Access Point; or (2) active scanning whereby the station attempts to find an Access Point by transmitting Probe Request frames and waiting for a Probe Response from the Access Point. Note that the Beacon frame is a periodic frame sent by the Access Point containing synchronization information.
Once the station has found an Access Point, in order to join the BSS, it must perform the Authentication Process which involves the exchange of information between the Access Point and the station, where each side shows knowledge of a shared credential(s).
Once authenticated, the station begins the Association Process which involves the exchange of information about the station and BSS capabilities. Only after the association process is complete, is the station permitted to transmit and receive data frames with the Access Point.
In implementing the WLAN protocol, communications devices often utilize so called WLAN profiles to aid in establishing connections between stations and access points. A wireless local area network profile defines the parameters for the connection between the station and WLAN networks including access points. Profiles typically include connection related information including, for example, SSID, connection type (i.e., open or shared key), security, authentication, encryption, WEP shared keys, key length, frequency bands, roaming enable/disable, SSID broadcasted, etc.
Wireless devices are typically battery operated. As such, conserving battery power is important as doing so allows the wireless device to operate for an extended period of time. To conserve battery power, the wireless device will typically enter a “sleep mode” when it is not actively participating in a communication. During this sleep mode the wireless device will still monitor activity on the WLAN to determine if it should “wake up” and enter into a communication.